Endless furnace and the method of utilizing same for dry process, vitreous enameling

ABSTRACT

A method for enamel coating metal objects by the dry or powdered process which comprises heating the metal object to a temperature of about 1,700*-1,800* F., uniformly distributing enamel powder over the surface of the object, and fusing the powder coating on the metal object; particularly wherein an endless enameling furnace is employed having an inner and outer periphery, and a plurality of ports positioned along said outer periphery to permit entry and removal of a workpiece to be placed in said furnace; whereby in the steps of the method above described, a relatively cold metal object is first introduced into the heated environment of the endless furnace, progressively advanced within the endless furnace while its temperature is elevated to that of the environment within the furnace, temporarily removed from the furnace through one of the ports in the outer periphery thereof to receive a coating of dry enamel powder, then reintroduced into the heated environment of the furnace and again progressively advanced therein whereby the said enamel coating is fused on the metal object, temporarily removed to receive a second coating of dry enamel powder, reintroduced into the heated environment of the furnace to fuse the second enamel coating on the metal object, and finally removed from the endless furnace and permitted to cool.

United States atent Gornall [54] ENDLESS FURNACE AND THE METHOD OF UTILIZING SAME FOR DRY PROCESS, VITREOUS ENAMELING [72] Inventor: Henry A. Gornall, Lyndhurst, Ohio [73] Assignee: Ferro Corporation, Cleveland, Ohio [22] Filed: Aug. 27, 1969 [21] Appl. No.: 853,336

[52] US. Cl ..ll7/23, 117/119.6, 117/129, 118/308, 263/7 [51] Int. Cl. ..B44d l/46, B44d l/094 [58] Field of Search ..117/23, 94, 119.6, 129; 263/7; 1 18/308 [56] References Cited UNITED STATES PATENTS 1,603,368 10/1926 Weil ..1 17/1 19.6 1,610,809 12/1926 Newman... ..263/7 2,264,499 12/1941 Bair ..118/308 2,388,611 11/1945 Hess ..117/129 3,058,443 10/1962 Paton 118/308 3,063,878 1 H1962 Wilson ..263/7 3,130,032 4/1964 Nitschke et a1. 263/7 3,131,918 5/1964 Fallon ..263/7 3,191,574 6/1965 Robertson ..118/308 3,490,753 1/ 1970 Frisch ..263/7 1 51 Mar. 14, 1972 FOREIGN PATENTS OR APPLICATIONS 6,712,672 3/1968 Netherlands ..l l7/23 Primary ExaminerWilliam D. Martin Assistant ExaminerRaymond M. Speer Attorney-Milton L. Simmons and Donald M. MacKay [5 7] ABSTRACT A method for enamel coating metal objects by the dry or powdered process which comprises heating the metal object to a temperature of about 1,7001,800 F., uniformly distributing enamel powder over the surface of the object, and fusing the powder coating on the metal object; particularly wherein an endless enameling furnace is employed having an inner and outer periphery, and a plurality of ports positioned along said outer periphery to permit entry and removal of a workpiece to be placed in said furnace; whereby in the steps of the method above described, a relatively cold metal object is first introduced into the heated environment of the endless furnace, progressively advanced within the endless furnace while its temperature is elevated to that of the environment within the furnace, temporarily removed from the furnace through one of the ports in the outer periphery thereof to receive a coating of dry enamel powder, then reintroduced into the heated environment of the fumace and again progressively advanced therein whereby the said enamel coating is fused on the metal object, temporarily removed to receive a second coating of dry enamel powder, reintroduced into the heated environment of the furnace to fuse the second enamel coating on the metal object, and finally removed from the endless furnace and permitted to cool.

7 E EPFE 1 P19980 5? ENDLESS FURNACE AND THE METHOD OF UTILIZING SAME FOR DRY PROCESS, VITREOUS ENAMELING This invention relates to a furnace ideally suited for the continuous dry process enameling of metal objects, particularly cast iron bathroom fixtures, and to a process for continuously coating and firing said metal objects to be enameled in a single, unitary, endless furnace. More particularly the furnace is endless or circular and having an inner and outer periphery, a plurality of ports or doors of a size sufficient to permit entry and removal ofa metal workpiece to be placed in said furnace, said ports positioned along said outer periphery in spaced relationship to each other, an internal radiant heat means, and internal means for advancing workpieces to be preheated and enameled.

Preferably the process contemplates electromechanical means for inserting and withdrawing metal workpieces from said furnace, and electromechanical means for dusting or applying the dry enamel powder to be fired. Other than the novel, endless aspect with spaced ports, the furnace of this invention is of conventional basic structure as employed for ceramic firing and is fitted with insulated fire brick or the like and contains muffles or radiant tubes and the like for providing radiant heat.

Enamel coating of metal objects by the dry or powder process comprises heating a metal object to a temperature of about l,700-1,800 F., uniformly distributing over the surface of the object an enamel powder which is to be coated thereon, and fusing the powdered metal object by heating it in a suitable furnace to a temperature of about 1,7001,800 F.

It is necessary to periodically remove the object from the furnace in order to apply the dry enamel powder, depending upon the number of coatings desired.

This has been handled by an operator called an Enameler using electromechanical means. Because of the physical requirements for the enameler, i.e., the ability to withstand high temperature, be able to insert and remove from the furnace objects of considerable weight by the use of a simple fork-like tool and have the ability to apply a uniform distribution of enamel powder over the metal object, it has been difficult to obtain enamelers and thus maintain good production and uniform application. For these reasons electromechanical means are preferably employed both to insert and remove objects from the furnace and also dust or apply the powder enamel. Means for enameling by the dry process is described in Netherlands Pat. No. 6,712,672, esp. FIG. 13 which patent is herein incorporated by reference. Means for dusting are also described and illustrated in said patent. Although for large and bulky objects such as bathtubs it is normally preferred to employ electromechanical means to handle such objects, for many applications requiring less skill and particularly concerning small objects such as lavatories and sinks, the use of an enameler is quite satisfactory.

While the aforesaid patent represents an advance in the art as to means for inserting, withdrawing, and dusting heavy bathtub objects, the straight line furnace described therein has certain deficiencies which are obviated by this invention. The primary defect is that in a straight line furnace it is necessary to remove the means for transporting the object to be enameled when the object is removed which results in a substantial amount of heat loss. Consequently, the transporting device must be reheated when it is returned to the furnace to transport a new object. The overlooking of the heat loss to trays, conveyor chains and rollers has caused important furnaces to fail to meet the capacity and fuel consumption guarantees, with disastrous results to the furnace builders who were responsible." Industrial Furnaces Vol. 1, 5th Ed., Trinks and Mawhinney, published by John Wiley 8L Sons, N.Y. In addition the heat loss is greater with a straight line furnace at the entrance and exit points since heat tends to radiate in a straight line. in the furnace ofthe invention, however, the heat tends to radiate around the axis ofthe furnace and not out the entrance or exit points. Further the endless furnace of the invention permits the furnace to be placed in a more compact area. Moreover when the same port is used both for loading and unloading, the same equipment or operator can be used to handle the object. When desired, however, objects can be placed in and removed from the furnace at a variety of locations depending upon the time and temperature requirements of the article to be fired and/or the equipment space and personnel requirements.

The invention is illustrated by the accompanying drawing FIG. 1, which is a schematic representation of a top view ofa furnace. A plurality of supports (trays) for carrying the pieces to be enameled are illustrated by the numbers 1 through 20. The means for moving the supports which is preferably a series of chain driven rollers is not illustrated. One can also employ, however, a conveyor belt or railroad type cars placed on rails or similar type means. As illustrated there are entrance and exit ports opposite trays 1, l0, l2, l4, l6, and 18. There can be more or less ports however, depending on the size of the furnace, the temperature and residence times employed, etc. The trays as illustrated are moving in a counterclockwise direction but they can be moved in the opposite direction as well. Workpieces are introduced at point I, removed at points 10 and 14 for dusting, reinserted at points 12 and 16 and finally removed at point 18 for cooling. The trays are not moved in the furnace at a constant rate but rather are allowed to remain opposite an exit or entry point for a time sufficient to remove and insert a workpiece. Accordingly, depending upon the size of the furnace, the residence time, temperature employed and the size of the workpiece, in many cases the workpiece can be removed for dusting and reinserted into the furnace before any workpieces in the furnace are advanced. Likewise for very large furnaces, the cycle can be completed in a quarter or half of the furnace and thus two or more entrance and terminal exit ports will be employed. in a preferred embodiment, heat loss is minimized at the ports by employing an air curtain when the doors are opened.

The following example will illustrate the invention in more detail.

EXAMPLE 1 As illustrated in FIG. 1, bathtubs to be enameled are introduced at point 1 and are withdrawn for cooling at point 18. The temperature of the furnace is automatically maintained between about l,700 and about 1,800 F. and the residence time for a tub is maintained between about 20 minutes and about 60 minutes excluding the time between removal at points 10 and 14 for dusting and reinsertion at points 12 and 16. The tubs are advanced such that a tub is stationary at each of the entrance and exit ports for a time between about /2 minute and about 1 /2 minutes to provide a preheating time of between about 18 and 24 minutes. The pieces are inserted and withdrawn by means ofa forklike device. Two dusting operations are employed to obtain a thick coating of enamel and a piece to be returned to the furnace after dusting is returned within about 1 minute after its removal.

In another embodiment of this invention the pieces to be coated are merely preheated in the circular furnace and removed for dusting and placed in another endless furnace or box furnace of the conventional type. By this method it is not necessary to strictly control the furnace conditions such that a piece is not baked for too long a period or reinserted in the furnace before being properly dusted. The difficulties are minimized, however, when the furnace is conducted according to Example 1 inasmuch as there are two dusting operations. In some cases one dusting operation will be sufficient.

What is claimed is:

1. In the method of enameling a metallic workpiece by the dry process, the steps of:

a. maintaining a substantially enclosed, endless heated ambient environment,

b. maintaining, by radiant means, at least one segment of said environment at a temperature of from about l,700 F. to about 1,800 E, which temperature represents the peak temperature range ofsaid environment,

c. introducing thereinto, at a first point along said continuous, enclosed environment, a relatively cold, metallic workpiece,

d. progressively advancing said workpiece within said environment from said first point and simultaneously therewith elevating the temperature of said workpiece to substantially the peak temperature ofsaid environment,

e. temporarily removing said workpiece at a second point along its line of progression. whereat said workpiece is at the temperature achieved in the preceding step, applying dry process, powdered porcelain enamel thereon before said workpiece has had an opportunity to substantially cool,

f. re-introducing said workpiece into said environment at a point no closer to said first point than said second point, and again progressively advancing same, in: substantially the same direction as in step (d) above, while simultaneously stabilizing the temperature of said workpiece within the peak temperature range of said environment, and fusing said porcelain enamel on said workpiece,

g. temporarily removing said workpiece a second time from said environment, at a third point along its line of progression, applying a second coating of dry process powdered porcelain enamel thereon,

h, re-introducing said workpiece into said environment at a point no closer to said second point than said third point, and again progressively advancing same, in substantially the same direction as in step (d), while simultaneously stabilizing the temperature of said workpiece within the peak temperature range of said environment, and fusing said second coating on said workpiece,

i. removing said coated workpiece from said environment at a fourth point adjacent said first point,

j, permitting said workpiece to cool to room temperature, to

produce a porcelain enameled metallic workpiece, 2. in the method of enameling a metallic workpiece by the dry process, the steps of:

a. maintaining a substantially enclosed, endless heated ambient environment,

b. maintaining, by radiant means, at least one segment of said environment at a temperature of from about l,700 F. to about l,800 P, which temperature represents the peak temperature range of said environment,

c. introducing thereinto, at a first point along said continuous, enclosed environment, a relatively cold, metallic workpiece,

d. progressively advancing said workpiece within said environment from said first point and simultaneously therewith elevating the temperature of said workpiece to substantially the peak temperature of said environment,

e. temporarily removing said workpiece at a second point along its line of progression, whereat said workpiece is at the temperature achieved in the preceding step, applying dry process, powdered porcelain enamel thereon before said workpiece has had an opportunity to substantially cool,

f. re-introducing said workpiece into said environment at a point no closer to said first point, than said second point, and again progressively advancing same, in substantially the same direction as in step (d) above, while simultaneously stabilizing the temperature of said workpiece within the peak temperature range of said environment, and fusing said porcelain enamel on said workpiece,

g. removing said coated workpiece from said environment at a third point adjacent said first point.

it. permitting said workpiece to cool to room temperature,

to produce a porcelain enameled metallic workpiece. 

2. In the method of enameling a metallic workpiece by the dry process, the steps of: a. maintaining a substantially enclosed, endless heated ambient environment, b. maintaining, by radiant means, at least one segment of said environment at a temperature of from about 1,700* F. to about 1,800* F., which temperature represents the peak temperature range of said environment, c. introducing thereinto, at a first point along said continuous, enclosed environment, a relatively cold, metallic workpiece, d. progressively advancing said workpiece within said environment from said first point and simultaneously therewith elevating the temperature of said workpiece to substantially the peak temperature of said environment, e. temporarily removing said workpiece at a second point along its line of progression, whereat said workpiece is at the temperature achieved in the preceding step, applying dry process, powdered porcelain enamel thereon before said workpiece has had an opportunity to substantially cool, f. re-introducing said workpiece into said environment at a point no closer to said first point, than said second point, and again progressively advancing same, in substantially the same direction as in step (d) above, while simultaneously stabilizing the temperature of said workpiece within the peak temperature range of said environment, and fusing said porcelain enamel on said workpiece, g. removing said coated workpiece from said environment at a third point adjacent said first point. h. permitting said workpiece to cool to room temperature, to produce a porcelain enameled metallic workpiece. 